An ice island four times the size of Manhattan broke off from one of Greenland's two main glaciers, scientists said Friday, in the biggest such event in the Arctic in nearly 50 years.

The new ice island, which broke off on Thursday, will enter a remote place called the Nares Strait, about 620 miles south of the North Pole between Greenland and Canada.

The ice island has an area of 100 square miles and a thickness up to half the height of the Empire State Building, said Andreas Muenchow, professor of ocean science and engineering at the University of Delaware.

Muenchow said he had expected an ice chunk to break off from the Petermann Glacier, one of the two largest remaining ones in Greenland, because it had been growing in size for seven or eight years. But he did not expect it to be so large.

"The freshwater stored in this ice island could keep the Delaware or Hudson Rivers flowing for more than two years," said Muenchow, whose research in the area is supported by the National Science Foundation.

"It could also keep all U.S. public tap water flowing for 120 days."

Global warming?
He said it was hard to judge whether the event occurred due to global warming because records on the sea water around the glacier have only been kept since 2003. The flow of sea water below the glaciers is one of the main causes of ice calvings off Greenland.

Scientists have said the first six months of 2010 have been the hottest globally on record. The El Nino weather pattern has contributed to higher temperatures, but many scientists say elevated levels of man-made greenhouse gases are pushing temperatures higher.

The initial discovery of the calving was made by Trudy Wohlleben of the Canadian Ice Service.

The ice island could fuse to land, break up into smaller pieces, or slowly move south where it could block shipping, Muenchow said.

The last time such a large ice island formed was in 1962 when the Ward Hunt Ice Shelf calved an island. Smaller pieces of that chunk became lodged between real islands inside Nares Strait.